The music shops in Chetumal and Belize City do not sell quality strings to begin with. They all seem to stock the cheap strings that break easily. My wife plays guitar and we have to have strings shipped in and we supply our friends here with them.
Thats why SimonB is correct...it wouldn't work...the store would have to compete with people bringing stuff in from the U.S. and couldn't have a markup large enough to make a go of it.
Since we are talking music, Guitar pics is another thing that was needed by Richard recently and not easily found in case someone happens to want to bring any for local musicians I am sure they would appreciate it.